Signature management

Each Magnetic Treatment Facility (MTF) comprises a set of coils to produce the de-magnetising field, power supplies, a control office and sensors to measure the vessel’s residual magnetism. We design and supply the magnetic treatment aspects of all types of MTF: ‘Drive-in, permanent installations;

• Over-run, permanent, seabed structures;
• Close wrap
• Fixed
• Semi-fixed
• Portable
• Land based for vehicles and equipment

We work closely with the selected civil engineering company to advise on the design, location and building materials used in permanent installations to ensure magnetic hygiene is considered from concept design to execution. We also provide consultancy services on request.

Whilst magnetic treatment and on-board degaussing systems reduce the vessel’s magnetic signature, it is equally important to know the magnetic signature of installed equipment.

This is particularly true for GRP or wooden hull vessels where the vessel’s magnetic signature is likely to be driven by installed equipment. We are experts in designing and supplying land-based magnetic management facilities.

We work closely with the customer to ensure that the chosen site is suitable (magnetically stable and quiet area); design a purpose built non-magnetic building and supply all the measuring equipment; survey and control all materials used in the facility construction; oversee the construction and installation of measurement coil assemblies; and install the magnetometers, data acquisition, computer and control systems, remote displays and CCTV system.

The Active Shaft Grounding (ASG) offerings from EMS are fully integrated with the advanced ICCP systems and report voltage readings and current outputs back to the advanced ICCP controller. This then passes the data to the ship's communications.

An ASG system can be installed to ensure low resistance between the rotating shaft and the hull. The ASG system uses slip-ring sensors connected to the shaft to measure the potential difference between the shaft and hull. This senses the variation in current along the shaft and then uses a power supply to draw proportional current through a second slip-ring assembly. This system works as a current by-pass for the shaft bearings. Essentially, it acts as a ‘short’ between ground and hull with any readable resistance measuring lower than 0.001 ohms. Since the ASG system constantly adjusts, the resistance will stay the same throughout a complete revolution of the shaft.

This low level of resistance results in reduced alternating electric and CRM field signatures levels. These levels are undetectable by most sensors used for mines and torpedoes. They will meet most AEP and ACRM signature limit requirements for an extended time period, as compared to PSG, before maintenance is needed.

The ability to automatically adjust to minimise shaft resistance and modulation results in less potential for damage to the shaft bearings.

Onboard degaussing (OBDG) systems are systems whose architectures can be tailored for specific ship missions, requirements and logistics.

OBDG Systems can be:

• simple systems that use cost and weight efficiency to meet specific signature requirements for a given vessel
• advanced degaussing (ADG) systems that minimise ship signatures and provide other signature modification capabilities
• highly advanced degaussing systems that provide closed-loop (CLDG) feedback control or technologically advanced current and power distribution networks and/or communications and control architectures

OBDG systems, ADG or otherwise, can have their power modules:

• fully distributed for maximum survivability/availability
• semi-distributed for optimisation of cost, weight and power
• centralised for maintenance optimisation

We offer these architecture options and can customise offerings to meet specific requirements for any ship class and offer all of these options as full US MIL-SPEC or NATO compliant.

The galvanic corrosion effect from ships is a result of the use of dissimilar metals. The seawater, propellers and hull act as the inside of a battery. The battery creates a current flow in the seawater from the steel hull to the non-ferrous propellers. An ICCP system designed by EMS consists of current anodes that surrender their current to the propeller in place of the steel-sacrificing current, thus inhibiting and stopping corrosion of the steel. This circuit inside the 'battery' is the mechanism for the creation of the Underwater Electric-field Potential (UEP) signature due to corrosion and the ICCP system.

The completion of the 'battery' circuit is the return current path from the propeller to the hull when no ICCP is present, or from the propeller to the anodes (or ICCP power supplies) with ICCP systems present. This circuit can be considered the circuit outside of the 'battery' and consists of the propeller shaft, the shaft bearings, the hull and the anode grounding circuit. This generation of current both in the seawater (inside the battery) and in the ship's propeller shafts and hull (outside the battery) is the mechanism for the creation of the Corrosion Related Magnetic (CRM) signature of the vessel.

We specialise in the design, manufacture and calibration of advanced ICCP systems that prevent the corrosion of the ship's hull and minimise the UEP and CRM signatures. This is achieved by the design and architecture of the total ICCP system and using the advanced ICCP system and by the use of advanced ICCP control algorithms.